Stereophonic sound enhancement system with reverberation chamber

ABSTRACT

The reverberation characteristics of an auditorium or music hall are improved by picking up the sound originating in the auditorium with microphones, and reproducing the sound in a second room having a more optimal reverberation characteristic. A second set of microphones in the second room picks up the sound and its reverberations for transmission to a group of loudspeakers in the auditorium, where it is blended with the original sound.

limited [72] Inventor John E. Volhmann Princeton, NJ.

[21] Appl.No. 783,618 [22] Filed Dec. 13, 1960 [45] Patented Oct. 19,1971 [73] Assignee RCA Corporation [54] STEEEOPHONIIC SOUND ENHANCEMENTSYSTEM WITH REVEIRBERATIION CHAMBER 6 Claims, 2 Drawing Figs.

[52] IU.S.CI 179/1J [51] int. Cl llll04r 5/02 [50] Field of Search179/1.6,

[56] References Cited UNITED STATES PATENTS 1,853,286 4/1932 Round eta1. 179/1 (.6) 2,421,424 6/1947 Kreuzer 179/1 (.6)

[ 1 3,0lldfi20 2,017,153 10/1935 Kellogg 179/100.1

2,107,804 2/1938 Roux et al.... 179/L6 3,024,309 3/1962 Kleis 179/1.6OTHER REFERENCES Stereophonic Localization: An Analysis of ListenerReactions to Current Techniques; Eargle, John M.; lRE Transactions onAudio; September- October, 1960; pp. 174- 177.

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Randall P. MyersAttorney-Eugene M. Whitacre a! Mama/ M/www STERIEUIPIHIQNIC SOUNDENHANCEMENT SYSTEM Wll'llill REVERBIERATION CHAMBER SOUND ENHANCEMENTThis invention relates to sound reproducing systems and moreparticularly to a system to provide for the enchancement of thereverberation characteristics of a music hall or auditori- A problemcommon to many music halls and auditoriums is that the reverberationtime of the hall auditorium may be too short. Reverberation time isdefined as the time it takes for a given sound intensity to decrease afixed amount. A hall with too short a reverberation time has beenreferred to as a dry hall and such a hall does not provide theappropriate acoustical characteristics for optimum presentation andrecording of music. Various methods and systems to solve this problemhave been attempted.

One system known in the prior art consists of transmitting sound from anauditorium to an acoustical chamber of small dimensions relative to theauditorium and then transmitting the reverberated sound from theacoustical chamber back to the auditorium. Such a system is disclosed inboux et al., US. Pat. No. 2,107,804. The disadvantages of this systemare that it provides the listener with a feeling that the sound isartificially reverberated or altered instead of naturally reverberated.This may be caused by the reverberated sound lacking spatialdistribution and directional illusion, or by the reverberated soundhaving an effective mean free path which is considerably different thanthe natural mean free path of the music hall. Mean free path is definedas the average distance sound travels between successive reflections ina chamber.

An object of this invention is to provide an improved system forpresenting or recording a sound program, such as music, in

'an auditorium with a given reverberation characteristic in a mannersuch that the auditorium appears to have enhanced reverberationcharacteristics.

A further object of this invention is to enhance the reverberationcharacteristics of a hall or chamber without significantly changingother acoustical characteristics of the hall or chamber.

In accordance with the invention, the natural reverberationcharacteristics of a secondary chamber is superimposed on thereverberation characteristics of a primary chamber in such a manner thatthe reverberation characteristics of both chambers are naturallyintegrated or blended together in the primary chamber with respect totime sequencing, spatial distribution, direction illusion, and amplitudelevels, and without amplifying the direct orchestral sounds ordetrimentally altering the inherent good acoustics (clarity, definition,blending, socalled presence, intimacy, etc.) of the early soundreflections in the primary chamber. The dimensions of the secondarychamber are such that the effective mean free path of the reverberatedsound is of the order of that of the primary chamber.

Various other objects and advantages will appear from the followingdescription of the several embodiments of the invention, and the novelfeatures will be particularly pointed out hereinafter in connection withthe appended claims.

The drawings diagrammatically represent different examples of means forcarrying out the invention.

FIG. l is a schematic diagram of a system for recording sound in anauditorium with enhanced reverberations; and

FIG. 2 is a schematic diagram of another embodiment of a system forrecording sound in an auditorium with enhanced reverberations.

Referring now to the drawings and in particular to FIG. 1, the musichall or primary chamber which has a reverberation time characteristicthat is not regarded as sufficiently long for the presentation orrecording of music comprises a stage portion 12 and an audience portionM. At least two pick-up devices or microphones 16, 18 are located in thearea of the audience portion 114 adjacent the stage portion 12 in aposition to pick up the direct sound wave fronts of the musicpresentation from the stage portion 112.

It will be understood that the microphones 116, 118 could also belocated on the stage portion 112, the exact location of the microphonebeing dependent on the location of the sound source (orchestra). A pairof microphones I6, 18 are connected to the respective input terminals20), 22 of a pair of amplifiers 24, 26 which may be located in the musichall 110 or exterior thereof. The output signals from the amplifiers 2d,26 are then respectively coupled to a pair of loudspeakers 28, 30located in a secondary chamber or room 32 which is separate from theprimary chamber 110. The loudspeakers 2b, 30 are distributed in thesecondary chamber 32 so as to reproduce stereophonically therein thesound wave fronts as they are picked up in the primary stage 110. Thisis accomplished by distributing loudspeakers 2b, 30 in the secondarychamber 32 in a similar or corresponding spatial relationship to thepositioning of microphones I6 and 28 in the primary chamber 110. Thesecondary chamber 32 has a reverberation time characteristic which ispreferably longer than that of the primary chamber, and is of a timeduration considered desirable for superposition in the primary chamber10 during the presentation of sound therein as will be hereinafterdescribed. The effective mean free path of the reverberated sound in thesecondary chamber 32 is of the same order as that of the primary chamberlltl. In other words, the average distance that a sound wave travelsbetween reflections in the secondary chamber, with or withoutsupplementary acoustic delay, is of the same order of magnitude as thatin the primary chamber. This aids in effecting a spatial distributionand directional illustration in the reverberated sound waves produced inthe secondary chamber 32. The total sound produced in the secondarychamber 32, which comprises the original sound introduced therein alongwith its increased reverberation, are picked up by a plurality ofmicrophones 3 1, 36, 38, M], 42, and M positioned within the secondarychamber 32 in an arcuate array as shown in FIG. I. The outputs from eachof the microphones 3 are coupled via respective amplifiers to, W, St),52, 5d, 56 to respective loudspeakers 5d, 60, '52, 64, 66 and 68, saidloudspeakers being located in the primary chamber lit] and within theaudience portion M of the primary chamber 10 so as to reproduce thereinthe reverberation sound wave fronts as they are picked up in thesecondary chamber 32.

In operation of the system, the microphones l6 and lb pick up primarilythe direct sound wave fronts from the stage area B2. The spacing of themicrophones l6 and lb permits the sound to be transduced in stereophonicrelation so that similar sound wave fronts can be recreated in thesecondary chamber 32 by loudspeakers 23 and 30. The direct andreverberated sound picked up by the microphones .3 in the secondarychamber 32 is amplified and reproduced by their associated loudspeakersin the primary chamber 10 at a level such that the sound appears to comefrom the stage area 112, and the reverberated sound from the secondarychamber 32 is smoothly blended with the natural reverberant sound in theprimary chamber lit).

For recording purposes, additional microphones 70, I2, 74$, 76, 78 and80 may be located on the stage l2 and audience M portions of the primarychamber lit). These microphones may be connected to respective inputterminals of a suitable recording apparatus indicated by the block at$2. Recording apparatus 82 may comprise means for transcribing the soundaudible in the primary chamber 20 and picked up by the microphones 70-30on to recording tape or phonograph records for commercial purposes.

The amplifiers shown in the drawing may include equalizers, filters andacoustic delay means. Equalizers may be pro vided to selectively varythe phase and/or amplitude of the signals processed therethrough.Filters may be used to filter out or attenuate certain frequencies asdesired. Acoustic delay means which may be electronic, mechanical, oracoustical may be employed to add additional time to delay to thesystem.

The secondary chamber may be any size or shape so long as the effectivemean free path, with or without supplementary acoustic delay of thereverberated sound is comparable to or of the same order of magnitude asthat of the primary chamber. Also, two or more secondary chambers may beconnected in series in order to further modify the reverberationcharacteristics of the primary chamber.

Referring now to the embodiment of FIG. 2, the system shown therein wasused to increase the reverberation time of the auditorium in the Academyof Music in Philadelphia, Pa. This auditorium, when used for recording,was though to have a dry sound and had a reverberation time of about 1.4seconds. With the system shown in FIG. 2, the reverberation time of theauditorium was increased to about 2.2 seconds. Specifically, withreference to FIG. 2, four microphones 90, 92, 94 and 96 were arranged onstage 99 of the Academy auditorium 100, in a position to pick up thedirect sound wave fronts of the music presentation from the stage. Soundpicked up by the microphones 90, 92, 94 and 96 was respectively coupledto amplifiers 102, 104, 106 and 108. The outputs from amplifiers 102 and104 were combined and fed to a first loudspeaker 110, and the outputsfrom amplifiers 106 and 108 combined and fed to a second loudspeaker112, both of said loudspeakers being located in the main ballroom of theAcademy which was used as the secondary chamber 114. Four microphones116, 118, 120 and 122 located in the secondary chamber 114 wererespectively coupled to amplifiers 124, 126, 128 and 130, the outputs ofwhich were combined as shown in FIGURE to provide four signals fordriving respective loudspeakers 132, 134, 136 and 138 in the audienceportion 98 of the Academy auditorium 100. For recording purposes, fourmicrophones 140, 142, 144 and 146, located on the stage portion 99 ofthe auditorium, were coupled to a recording apparatus 148. It was foundthat the size and acoustical characteristics of the ballroom, along withthe arrangement of the loudspeakers and microphones in the auditorium,and the ballroom, were such as to produce a realistic reproduction inthe auditorium with an enhanced reverberation effect. The blending orintegration of the sound originating in the auditorium with itsreverberations in the ballroom was accomplished without affecting thetime sequence, spatial distribution, and directional illustration of themusic. The enchancement process was carried out without increasing theeffective loudness of the direct orchestral sound and without alteringthe inherent good acoustical characteristics of the auditorium. Thesound was transmitted from the auditorium to the ballroom and back againto be blended with the original sound so as to reinforce and enhance thesound as it was heard and recorded throughout the auditorium.

In addition to the embodiments shown, a variation of the presentinvention may comprise the use of plurality of secondary chambers alongwith means for selecting which secondary chambers are to be used toenhance the sound in the primary chamber. The reverberationcharacteristics of the total sound originating in the primary chambermay be varied by selecting a different secondary chamber into which thissound is to be fed. The microphones in the primary chamber may be soarranged with the selecting means so that the various sound transducedby the individual microphones may be fed to different secondarychambers. The sounds reverberated in the secondary chambers may beselectively fed to various loudspeakers arranged in the primary chamber.This embodiment will allow the reverberation of a particular sound inthe primary to be altered without changing the reverberation of theother sounds.

What is claimed is:

l. A sound enchancement system comprising:

a primary chamber,

a secondary chamber having selected physical dimensions such that themean free path of sound in said secondary chamber is of the same orderof magnitude as the mean free path of sound in said primary chamber,

means for transmitting electrical signals representative of chamber andconverting said electrical signals into sound,

said means for transmitting electrical signals representative of soundin said primary chamber to said second chamber comprising a plurality ofstereophonically related channels, and

means for transmitting electrical signals representative of the soundalong with its reverberations from said secondary chamber to saidprimary chamber and converting said electrical signals into sound, saidmeans for transmitting electrical signals representative of said soundalong with its reverberations from said secondary chamber to saidprimary chamber comprising a plurality of stereophonically relatedchannels, thereby to enhance the acoustical characteristics of saidprimary chamber.

2. A sound enchancement system as defined in claim 1 wherein,

said secondary chamber has a reverberation time which is longer than thereverberation time of said primary chamber.

3. A sound enchancement system as defined in claim 1 wherein,

said means for transmitting electrical signals representative of saidsound in said primary chamber to said secondary chamber further includespickup means in said primary chamber located near to where the soundoriginates from so as to pick up a direct sound wave front.

4. A sound enchancement system comprising:

a primary chamber;

a secondary chamber, having a reverberation time longer than thereverberation time of said primary chamber and having selected physicaldimensions such that the mean free path of sound in said secondarychamber is of the same order of magnitude as the means free path ofsound in said primary chamber;

first means for transmitting electrical signals representative of soundis said primary chamber to said secondary chamber comprising a pluralityof stereophonically related channels and including pickup means, locatedin said primary chamber near to where the sound originates, for pickingup a direct sound wave front, said first means further includingreproducing means, located near wall in said secondary chambercorresponding in spatial array to the positioning of said pickup meansin said primary chamber, for reproducing said sound-wave front of saidprimary chamber in said secondary chamber; and

second means for transmitting electrical signals representa tive of thesound along with its reverberations from said secondary chamber to saidprimary chamber and converting said electrical signals into sound,thereby to enhance the acoustical characteristics of said primarychamber, said second means comprising a plurality of stereophonicallyrelated channels.

5. A sound enchancement system as defined in claim 4 wherein,

said means for transmitting electrical signals representative of saidsound along with its reverberations from said secondary to said primarychamber further includes in said secondary chamber, pickup means locatednear walls other than from where said sound wave front is originallyintroduced therein.

6. A sound enhancement system as defined in claim 5 wherein,

said means for transmitting electrical signals representative of saidsound along with its reverberations from said secondary to said primarychamber further includes in said primary chamber reproducing meanslocated near walls other than from where said sound wave frontoriginates.

UNITED STATES PATENT OFFICE CERTlFlCATE ()F CORRECTION Patent 3,614,320Dated October 19, 1971 Inventor(s) John Volkmann It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In Column 1, line 1.0, following "hall" insert or line 23, delete "boux"and insert Roux Column 2, line 17, delete "28" and insert 18 line 29,delete "illustration" and insert illusion line 62, delete "20" andinsert 10 line 71, that portion reading "time to delay should read timedelay Column 3, line B, delete "though" and insert thought line 26, thatportion reading "in FIGURE" should read in the FIGURE line delete"illustration" and insert mm illusion Column 4, line 34, delete "means"and insert mean """u Signed and sealed this 11th day of April 1972.

(SEAL) Attestr EDWARD I LFLETCHEQ, JR. ROBERT GOTI'SCHALK AttestingOfficer Commissioner of Patents RM poqoso H0459) usgoMM-oc sows-pe U 5GOVERNMENT PRINYING OFFICE I969 0-366-334

1. A sound enchancement system comprising: a primary chamber, asecondary chamber having selected physical dimensions such that the meanfree path of sound in said secondary chamber is of the same order ofmagnitude as the mean free path of sound in said primary chamber, meansfor transmitting electrical signals representative of sound in saidprimary chamber to said secondary chamber and converting said electricalsignals into sound, said means for transmitting electrical signalsrepresentative of sound in said primary chamber to said second chambercomprising a plurality of stereophonically related channels, and meansfor transmitting electrical signals representative of the sound alongwith its reverberations from said secondary chamber to said primarychamber and converting said electrical signals into sound, said meansfor transmitting electrical signals representative of said sound alongwith its reverberations from said secondary chamber to said primarychamber comprising a plurality of stereophonically related channels,thereby to enhance the acoustical characteristics of said primarychamber.
 2. A sound enchancement system as defined in claim 1 wherein,said secondary chamber has a reverberation time which is longer than thereverberation time of said primary chamber.
 3. A sound enchancementsystem as defined in claim 1 wherein, said means for transmittingelectrical signals representative of said sound in said primary chamberto said secondary chamber further includes pickup means in said primarychamber located near to where the sound originates from so as to pick upa direct sound wave front.
 4. A sound enchancement system comprising: aprimary chamber; a secondary chamber, having a reverberation time longerthan the reverberation time of said primary chamber and having selectedphysical dimensions such that the mean free path of sound in saidsecondary chamber is of the same order of magnitude as the means freepath of sound in said primary chamber; first means for transmittingelectrical signals representative of sound is said primary chamber tosaid secondary chamber comprising a plurality of stereophonicallyrelated channels and including pickup means, located in said primarychamber near to where the sound originates, for picking up a directsound wave front, said first means further including reproducing means,located near wall in said secondary chamber corresponding in spatialarray to the positioning of said pickup means in said primary chamber,for reproducing said sound-wave front of said primary chamber in saidsecondary chamber; and second means for transmitting electrical signalsrepresentative of the sound along with its reverberations from saidsecondary chamber to said primary chamber and convertIng said electricalsignals into sound, thereby to enhance the acoustical characteristics ofsaid primary chamber, said second means comprising a plurality ofstereophonically related channels.
 5. A sound enchancement system asdefined in claim 4 wherein, said means for transmitting electricalsignals representative of said sound along with its reverberations fromsaid secondary to said primary chamber further includes in saidsecondary chamber, pickup means located near walls other than from wheresaid sound wave front is originally introduced therein.
 6. A soundenhancement system as defined in claim 5 wherein, said means fortransmitting electrical signals representative of said sound along withits reverberations from said secondary to said primary chamber furtherincludes in said primary chamber reproducing means located near wallsother than from where said sound wave front originates.